Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform

1. Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform Jerry Chun-Pai Jun, Jenshan Lin, Hung-Tan Wang Fan Ren, Stephen Pearton and Toshikazu Nishida University of Florida

2. Motivation Behind a Self-Powered Wireless Hydrogen Sensing Platform • Popular topic due to need of inexpensive sensor devices requiring minimal maintenance to monitor harsh and dangerous environs. • Growing interest in hydrogen as a fuel cell, which is dangerous if not properly contained. • Combustion gas detection in Spacecrafts and Proton-Exchange Membrane (PEM) Fuel Cells • Greater than 4% of hydrogen concentrations are explosive.

3. Limitations Of Sensor Development • Limitations of Energy Harvesting Devices • Limitations of Low-Power and Low- Voltage Commercial Components • Limitations of a Wireless System • Wireless Channel Estimation • FCC Regulations

4. Solar Energy Harvesting Solar Cells are a mature commercial Product Dependent upon real-time lighting and temperature conditions Pulse Resonant Power Converter Self-powered and self controlled Convert input voltage of 0.8-1.2V to steady 2V output Energy Harvesting Techniques Vibration Energy Harvesting • Collection of energy proportional to volume of device • Limited to magnitude and frequency of vibrations • For Proof of Concept • PSI D220-A4-203YB Double Quick Mounted Y-Pole PZT Device • Direct Charging Circuit

5. Energy Harvesting Techniques cont. Solar Energy Harvesting Vibration Energy Harvesting IXOLAR XOD17-04B Solar Cell Four mounted PSI D220-A4-203YB Double Quick Mounted Y-Pole Bender (a) Direct Charging Circuit (b) Pulse Resonant Power Converter Functional Block Diagram (a) Bare die photo (b)

6. ZnO currently used for detection of humidity, UV light and gas detection Easy to synthesize on a plethora of substrates Bio-safe characteristics Large chemically sensitive surface to volume ratio If coated with Pt or Pd, can increase device’s sensitivity to hydrogen High compatibility to microelectronic devices ZnO Nano-Rods as a Sensing Mechanism Schematic of Multiple ZnO Nano-Rods Close-Up of Packaged ZnO Nano-Rod Sensor

7. Sputtered with Pt coatings of approximately 10 Å in thickness Show no response to the presence of O2 and N2 at room temperature Pt increases conductivity of Nano-Rods Up to 8% change in resistance after 10 min. exposure to 500 PPM of hydrogen Greater than 2% change in resistance after 10 min exposure to 10 PPM of hydrogen 90% recovery within 20 seconds upon removal of hydrogen from the ambient Pt-ZnO Nano-Rod Sensors Pt-coated ZnO Nano-Rod - Relative Resistance Change for Various Hydrogen Concentrations

8. Comparison of ZnO Nano-Rods Coated with Different Metals Relative Resistance Change for Various Metal-coated ZnO Nano-Rods

9. Wheatstone Resistive Bridge Can limit current consumption of resistive bridge Best way to detect changes in resistance Difference Amplifier Using differential architecture of operational amplifier to subtract difference at input, and apply gain Form of differential measurement Differential Measurement

10. Provides High Impedance Input Buffers isolate V1 and V2 from resistive network of difference amplifier Buffers and provides gain before difference amplifier Gain can be easily adjusted by varying a single resistor, Rg. Instrumentation Amplifier

11. Since Pt-ZnO Nano-Rod devices react to both hydrogen and temperature, the use of a passivated ZnO as a reference resistor can mitigate the temperature dependency of the differential Detection Circuit. Rbias used to limit current flowing into both legs of resistive bridge Maintains concept of a differential measurement Instrumentation Amplifier helps balance input offset voltages, while providing gain, and conditioning signal for ADC Differential Detection Circuit

12. Fabricated Pt-ZnO Nano-Rod for Use in Differential Detection Circuit

13. Fabricated Differential Detection Circuit

14. Fabricated Differential Detection Circuit

15. Low-Voltage Low-Active Current Low-Sleep Current Onboard Memory Onboard ADC Serial Output Reprogrammable Microcontroller Selection REQUIREMENTS Features of Texas Instruments’ MSP430F1232IPW

16. Runs through state until a discernable presence of hydrogen is detected. Once hydrogen is detected, microcontroller forces RF front-end to transmit an emergency pulse to the central monitoring station before returning back to an idle mode. Hydrogen threshold level is at far less than dangerous levels Runs through states until a discernable presence of hydrogen is detected. Once threshold is detected, the data from the ADC is queued onto the serial output port of the microcontroller to be transmitted. Once transmitted, state is reset to sleep For constant tracking of hydrogen levels Microcontroller Operation Level Monitoring State Machine Data Transmission State Machine

17. RF Power Amplifiers and Oscillators have efficiencies of 50% at best Low parts count Low Duty-Cycle, Low Data Rate. Expend energy only for transmission of Data Low complexity Selection of a Modulation Technique MODULATION REQUIREMENTS Comparison of Complexity between π/4- DQPSK and OOK

18. 300 MHz Ming TX-99 Onboard antenna OOK Modulation Low Part Count Low Complexity Tunable Frequency Colpitts Oscillator Selection of RF Transmitter (1) Ming TX-99 Transmitter in OOK Mode Ming TX-99 Transmitter

19. Selection of RF Receiver (1) 300 MHz Ming RE-99 • Onboard antenna • External Antenna Tap • Low Part Count • Low Complexity • Tunable Frequency • Envelope Detection • Little Documentation Ming RE-99 Receiver Schematic Ming RE-99 Receiver

20. Distance Measurements Received Power vs. Distance With Reference to Room Shape • Shape of room resulted in a wave-guide effect at 10 meters • Last successful data transfer occurred at 19.4 m • Received power at this distance was approximately -70 dBm • Can assume Ming RE-99 Receiver sensitivity is approximately -70 dBm

21. At the time, used Ming RE-99 Receiver NI USB-6008 DAQ device for power to Receiver, and ADC to capture data Powered from HP Laptop’s USB Port Running LabVIEW 7.1 Moving Average Filter to differentiate data “pulse” from noise Central Monitoring Station Moving Average Filter Example Labview Block Diagram Code and Labview Front Panel Gui

22. Full System Integration and Testing or Schematic of Hydrogen Chamber Schematic of Hydrogen Chamber

23. Future Work: New Receiver Linx Technologies RXM-315-LR • Replacement for Ming RE-99 since Rayming Corp. went out of business • OOK Modulation • Low Part Count • Low Complexity • RSSI/PDN • -112 dBm Sensitivity System Level Architecture for RXM-315-LR Pin-Out of RXM-315-LR receiver, and receiver test board, shown with SPLATCH antenna

24. Linx Technologies ANT-315-SP ‘SPLATCH’ Style Antenna Grounded Line, Microstrip Monopole Antenna After matching, -9dB gain, trade off for low-profile antenna 5 MHz -10 dB BW, Center Frequency = 315 MHz Future Work: Low-Profile Antenna ‘SPLATCH’ dimensions, matched S-parameters Antenna Test Board w/ Matching Circuit

25. Mapping (n) source bits to message with a maximum of 2, or 3 “high” bits Example: 6 source bits 6 source bits = 64 messages (symbols)Find Codeword of length (m) that allow for 64 symbols, with a maximum of 3 high bits. 64 = mC3 + mC2 + mC1 + mC0 ; m = 7 Power Reduction Assumptions: for now, all source code symbols have equal probability of occurrences, and power is only consumed with the transmission of a high bit. So, Power Consumption Reduction is: By using a minimum energy coding technique, we can expect to reduce the power required to transmit an un-coded message by 20 to 40 percent. Future Work: Minimum Redundancy Minimum Energy Coding Proposed Source Coding Technique

26. Minimum Redundancy Minimum Energy Coding (cont.)

27. Conclusions • Successfully designed a low-power sensor interface for the Pt-ZnO Nano-Rod hydrogen sensing mechanism • In conjunction with the microcontroller, RF transmitter, and separate energy harvesting techniques, were successful in detecting and reporting the presence of 500 PPM of H2 in N2. (.05%) using Pt-ZnO Nano-rods as our sensing mechanism • Energy harvesting techniques include solar and vibration energy devices.